Torsional vibration damper

ABSTRACT

A torsional vibration damper having enhanced vibration damping performance is provided. The torsional vibration damper comprises: a vacant area existing between an outer circumference of the sun gear and an inner circumference of the ring gear outside of a revolving range of the planetary gears revolved as a result of relative rotation between the sun and the ring gear; and a mass increasing portion that is formed on the rotary member other than an input element and an output element within the vacant area in such a manner as to protrude from the rotary member.

CROSS-REFFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.15/082,076 filed Mar. 28, 2016, which claims the benefit of JapanesePatent Application No. 2015-068124 filed on Mar. 30, 2015 with theJapanese Patent Office, the disclosures of which are incorporated hereinby reference in its entirety.

BACKGROUND Field of the Invention

The present invention relates to the art of a vibration damper forsuppressing torque pulses (i.e., vibrations) by an inertial torque.

Discussion of the Related Art

U.S. Pat. No. 5,863,274 describes a torsional vibration dampingapparatus comprising a planetary transmission in which a sun gear servesas an input element, and a carrier or a ring gear serves as an outputelement. In the planetary transmission, the sun gear is connected to afirst mass, and the carrier or the ring gear is connected to a secondmass. According to the teachings of U.S. Pat. No. 5,863,274, coilsprings are interposed between any of two rotary elements of theplanetary transmission in such a manner as to permit an angulardisplacement therebetween to an extent which depends upon the extent ofdeformation of the coil springs.

The planetary gear unit used in a vibration damper is also describede.g., in JP-A-2009-14022 and JP-A-2010-1905. In the inertia devicetaught by JP-A-2009-14022, the planetary gear unit is used to obtain alarge inertia force by increasing rotational speed of an inertia ring tobe higher than an input speed. In turn, in the rotation fluctuationreduction device taught by JP-A-2010-1905, one of rotary elements of theplanetary gear unit is connected to an output shaft of an engine toserve as an input element, other rotary element is attached to aninertial mass, and still another rotary element is selectively halted bya brake. According to the teachings of JP-A-2010-1905, an inertia torquecounteracting torsional vibrations of the output shaft can be changed byhalting a rotation of predetermined rotary element by the brake.

In the above-explained prior art documents, an inertial forcecounteracting vibrations is established by an inertial mass connected toany of the rotary elements of the planetary gear unit, and such inertialforce can be increased by enlarging the inertial mass. According to theteachings of the above-explained prior art documents, however, theinertial masses are arranged in an axial direction of the planetary gearunit, and hence an axial length of the planetary gear unit may beelongated if the inertial masses are enlarged. Consequently, thevibration damping device may not be fitted into a powertrain easily.

SUMMARY

Aspects of the present invention have been conceived noting theforegoing technical problems, and it is therefore an object of thepresent invention is to provide a torsional vibration damper in which avibration damping performance in a low speed range is enhanced withoutbeing elongated in an axial direction.

The torsional vibration damper according to the preferred examplecomprises a planetary unit that performs a differential action among asun element as a rotational center element, a ring element arrangedconcentrically with the sun element, and a carrier element supportingplanetary elements interposed between the sun element and the ringelement in a rotatable and revolvable manner. In the planetary unit, anyof the sun element, the ring element and the carrier element serves asan input element to which torque is applied, and any of another rotaryelement serves as an output element. In addition, the input element isconnected to the output element through an elastic member while beingallowed to rotate relatively with each other. In order to achieve theabove-explained objective, according to the preferred embodiment of thepresent application, the torsional vibration damping device is providedwith: a vacant area that exists between an outer circumference of thesun element and an inner circumference of the ring element outside of arevolving range of the planetary gears revolved as a result of relativerotation between the sun element and the ring element; and a massincreasing portion that is formed on the rotary member other than theinput element and the output element within the vacant area in such amanner as to protrude from the rotary member.

In a non-limiting embodiment, a planetary gear unit having a sun gearserves as the sun element, a ring gear serves as the ring element,planetary gears serve as the planetary elements, and a carrier serves asthe carrier element may be used as the planetary unit. In this case, themass increasing portion may be formed on the sun gear.

In the torsional vibration damper according to the present application,the input element and the output element connected through the elasticmember are rotated relatively by pulsation of torque applied to theinput element. Consequently, the remaining rotary element is rotated bya differential action of the planetary unit to establish an inertialforce counteracting the torque pulse in accordance with a mass thereof.That is, the rotary element other than the input element and the outputelement serves as an inertial mass to suppress torsional vibrations.According to the present application, a mass of the rotary memberserving as an inertial mass is increased by the mass increasing portionso that vibration damping performance of the torsional vibration dampercan be enhanced especially in a low speed range. In addition, the massincreasing portion is formed on the rotary member other than the inputelement and the output element within the vacant area where theplanetary gears do not rolls thereon even if the sun element and thering element are rotated relatively by pulsation of the torque appliedto the input element. According to the present application, therefore, amass of the rotary element serving as an inertial mass can be increasedwithout elongating an axial length of the planetary unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of exemplary embodiments of thepresent invention will become better understood with reference to thefollowing description and accompanying drawings, which should not limitthe invention in any way.

FIG. 1a is a front view of the planetary unit according to the preferredembodiment;

FIG. 1b is a cross-sectional view of the planetary unit along the b-bline in FIG. 1 a;

FIG. 2a is a skeleton diagram showing the planetary unit arranged in apower train in which the ring gear serves as an input element and thecarrier serves as an output element;

FIG. 2b is a skeleton diagram showing the planetary unit arranged in apower train in which the ring gear serves as an output element and thecarrier serves as an input element;

FIG. 3a is a front view of the mass increasing portion formed integrallywith the sun gear;

FIG. 3b is a cross-sectional view of the mass increasing portion alongthe b-b line in FIG. 3 a;

FIG. 4a is a front view of the mass increasing portion attached to thesun gear by a bolt or a rivet;

FIG. 4b is a cross-sectional view of the mass increasing portion alongthe b-b line in FIG. 4 a;

FIG. 5 is a graph indicating vibration damping performances of thevibration damper according to the preferred embodiment and theconventional vibration damper;

FIG. 6a is a front view of the planetary unit according to anotherembodiment;

FIG. 6b is a cross-sectional view of the planetary unit according toanother embodiment along the b-b line in FIG. 6 a;

FIG. 7a is a skeleton diagram showing the planetary unit according toanother embodiment arranged in a power train in which the ring gearserves as an input element and the sun gear serves as an output element;

FIG. 7b is a skeleton diagram showing the planetary unit according toanother embodiment arranged in a power train in which the ring gearserves as an output element and the sun gear serves as an input element;

FIG. 8a is a front view of the planetary unit according to still anotherembodiment;

FIG. 8b is a cross-sectional view of the planetary unit according tostill another embodiment along the b-b line in FIG. 8 a;

FIG. 9a is a skeleton diagram showing the planetary unit according tostill another embodiment arranged in a power train in which the sun gearserves as an input element and the carrier serves as an output element;and

FIG. 9b is a skeleton diagram showing the planetary unit according tostill another embodiment arranged in a power train in which the sun gearserves as an output element and the carrier serves as an input element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The preferred embodiments of the present application will now beexplained in more detail with reference to the accompanying drawings.Referring now to FIG. 1, there is shown one example of the planetaryunit 1 as a main part of the torsional vibration damper that is adaptedto perform a differential action among three rotary elements. Forexample, a planetary gear unit and a planetary roller unit may be usedas the planetary unit 1. Specifically, the planetary unit comprises asun element 2 as a rotational center element, a ring element 3 arrangedconcentrically with the sun element 2, a plurality of planetary elements4 interposed between the sun element 2 and the ring element 3, and acarrier element 5 supporting the planetary element 4 in a rotatable andrevolvable manner. Given that the planetary gear unit is used as theplanetary unit 1, the sun element 2 is a sun gear as an external gear,the ring element 3 is a ring gear as an internal gear, the planetaryelements 4 are pinion gears, and the carrier element 5 is a carrier. Bycontrast, given that the planetary roller unit is used as the planetaryunit 1, the sun element 2 is a sun roller having a rolling surface onits outer circumferential face, the ring element 3 is a ring rollerhaving a rolling surface on its inner circumferential face, theplanetary elements 4 are cylindrical or column pinion rollers, and theplanetary elements 4 interposed between the sun roller and the ringroller are supported by a carrier 5. In the planetary roller unit, thepinion rollers have to be clamped tightly by the sun roller and the ringroller so as to ensure a desired torque transmitting capacity. Bycontrast, in the planetary gear unit, the pinion gears mesh with the sungear and the ring gear so that the desired torque transmitting capacityis ensured. Optionally, a double-pinion planetary gear unit may also beused as the planetary unit 1 according to need.

Turning to FIG. 2, there is shown an example of the torsional vibrationdamper arranged in a predetermined powertrain in which a single-pinionplanetary gear unit is used as the planetary unit 1. In the exampleshown in FIG. 2a , specifically, the ring gear 3 serves as an inputelement, the carrier 5 serves as an output element, and the ring gear 3is connected to the carrier 5 through a spring damper 6 as the claimedelastic member. In the example shown in FIG. 2a , therefore, the ringgear 3 and the carrier 5 are allowed to rotate relatively with eachother within a predetermined angle governed by a structure of the springdamper 6, and an elastic force of the spring damper 6 counteracts to atorque applied to the ring gear 3. The ring gear 3 is also connected toa prime mover (e.g., an internal combustion engine) 7, and the carrier 5is also connected to a driven member 8 such as a transmission. That is,pulsed torque is applied to the ring gear 3 and the carrier 5.

Specifically, when a torque of the prime mover 7 is applied to the ringgear 3, the carrier 5 is subjected to a reaction of the torque rotatingthe driven member 8. Consequently, the ring gear 3 and the carrier 5 arerotated relatively with each other while compressing the spring damper 6in accordance with the compressing load. In this situation, the sun gear2 as a rotational center is also rotated in accordance with an angle ofrelative rotation between the ring gear 3 and the carrier 5. If thetorque of the prime mover 7 applied to the ring gear 3 is stable, theplanetary unit 1 is rotated integrally to deliver the torque to thedriven member 8.

The compression force (i.e., a torsional force) is changed by pulsationof the torque applied to the ring gear 3 thereby causing a relativerotation between the ring gear 3 and the carrier 5. Since such relativerotation between the ring gear 3 and the carrier 5 is caused by thetorque pulse, an angle of the relative rotation between the ring gear 3and the carrier 5 is rather small. In this situation, therefore, thepinion gears 4 revolve around the sun gear 2 only within a predeterminedangle. A vacant area θ as an unused area of the sun gear 2 where thepinion gear 4 does not roll thereon is not involved directly in a torquetransmission and a differential rotation but involved in maintenance ofstrength and shape of the sun gear 2.

As described, the sun gear 2 is rotated or reciprocated as a result ofthe relative rotation between the ring gear 3 and the carrier 5 withinthe predetermined angle. Consequently, an inertial torque is establishedby such rotation of the sun gear 2 in accordance with an angularvelocity and a mass of the sun gear 2. In the planetary unit 1 shown inFIGS. 1 and 2, a mass increasing portion 9 is formed at least partiallywithin the vacant area θ of the sun gear 2 in such a manner as toprotrude radially outwardly. For example, as illustrated in FIGS. 3a and3b , the mass increasing portion 9 may be formed by partially expandingan outer circumference of the sun gear 2 to increase a thickness thereofinstead of forming the teeth 2 a. Alternatively, as illustrated in FIGS.4a and 4b , the mass increasing portion 9 may also be formed byattaching a mass piece having a thickness higher than a height of eachtooth 2 a to the outer circumference of the sun gear 2 by a rivet or abolt 10. In the planetary unit 1, therefore, a mass of the sun gear 2per unit of circumferential length can be increased at the massincreasing portion 9 to be larger than that of the remaining portion. Inaddition, since the mass increasing portion 9 is formed by partiallyexpanding the sun gear 2 radially outwardly in the planetary unit 1, amass of the sun gear 2 can be increased without elongating an axiallength of the planetary unit 1.

In the torsional vibration damper thus formed by the planetary unit 1and the spring damper 6, the ring gear 3 and the carrier 5 are rotatedrelatively from each other within the predetermined angle by a pulsationof torsional torque applied to the spring damper 6 resulting frompulsation of the torque applied to the ring gear 3. Consequently, thesun gear 2 is oscillated within the predetermined angle by thedifferential action of the planetary unit 1, and vibrations are dampedby the inertial torque resulting from oscillation of the sun gear 2.Such vibration damping performance of the sun gear 2 can be enhancedwithin the low speed range by increasing a mass of the sun gear 2.Turning to FIG. 5, there is shown a comparison result of the vibrationdamping performance between the torsional vibration damper according tothe preferred embodiment and the conventional torsional vibrationdamper. In FIG. 5, the dashed curve represents pulsation of torqueaccording to the first comparison example in which only the springdamper 6 is used in the powertrain to damp vibrations, the thinner curverepresents pulsation of torque according to the second comparisonexample in which the conventional planetary unit without having the massincreasing portion 9 is used in the powertrain to damp vibrations, andthe thicker line represents pulsation of torque according to thepreferred embodiment. In FIG. 5, specifically, the horizontal axisrepresents an engine speed, and the vertical axis represents a pulsationof torque (i.e., a propagation gain of vibration), and the dashedhorizontal line represents a criterion of acceptable pulsation oftorque. As can be seen from FIG. 5, vibration damping performance of thetorsional vibration damper according to the preferred embodiment isobviously enhanced within the low speed range of the engine.

Turning back to FIG. 2b , there is shown a modification example of thetorsional vibration damper. In the embodiment shown in FIG. 2b , theinput element and the output element are switched. Specifically, thering gear 3 is connected to the driven member 8 to serve as the outputelement, and the carrier 5 is connected to the prime mover 7 to serve asthe input element. In the embodiment shown in FIG. 2b , a relativerotation between the carrier 5 and the ring gear 3 is caused bypulsation of the torque applied to the spring damper 6 resulting frompulsation of input torque to the ring gear 5, and consequently the sungear 2 is oscillated within the predetermined angle. Thus, vibrationsmay also be damped by the inertial torque resulting from oscillation ofthe sun gear 2 without extending the axial length of the planetary unit1.

In the torsional vibration damper, the mass increasing portion 9 mayalso be formed on the rotary elements of the planetary unit 1 other thanthe sun gear 2. Turning to FIG. 6, there is shown another example of thetorsional vibration damper in which the mass increasing portion 9 isformed on the carrier 5. Specifically, the carrier 5 supports theequally-spaced pinion gears 4 in a rotatable and revolvable manner, andhence each portion of the carrier 5 between the pinion gears 4 is notbrought into contact to other members. That is, such clearance betweenthe pinion gears 4 serves as the vacant area θ that is not involved inthe differential action. According to the embodiment shown in FIG. 6,the mass increasing portion 9 is formed on the carrier 5 within thevacant area θ in such a manner to protrude toward the sun gear 2 and thering gear 3. As the foregoing embodiment, the mass increasing portion 9may be not only formed integrally with the carrier 5 but also attachedto the carrier 5 by a welding method or by a screw. If the carriers 5are arranged on both axial sides of the planetary unit 1, the massincreasing portion 9 may also be interposed between the carriers 5.

Thus, according to the embodiment shown in FIG. 6, the carrier 5 servesas an inertial mass together with the mass increasing portion 9 tosuppress vibrations. In this case, as shown in FIG. 7a , the ring gear 3may be connected to the prime mover 7 to serve as the input element, thesun gear 2 may be connected to the driven member 8 to serve as theoutput element, and the spring damper 6 may be interposed between thesun gear 2 and the ring gear 3. Alternatively, as shown in FIG. 7b , thering gear 3 may also be connected to the driven member 8 to serve as theoutput element, the sun gear 2 may also be connected to the prime mover7 to serve as the input element, and the spring damper 6 may beinterposed between the sun gear 2 and the ring gear 3.

Turning to FIG. 8, there is shown still another example of the torsionalvibration damper in which the mass increasing portion 9 is formed on thering gear 3. As described, the pinion gears 4 revolve only withinpredetermined areas, and each area in an inner circumference of the ringgear 3 that is not brought into engagement with the pinion gear 4 servesas the vacant area θ. According to the embodiment shown in FIG. 8,therefore, the mass increasing portion 9 is formed on the innercircumference of the ring gear 3 within the vacant area θ to protruderadially inwardly. As the foregoing embodiment, the mass increasingportion 9 may be not only formed integrally with the carrier 5 but alsoattached to the ring gear 3 by a fixing means such as a rivet and abolt.

Thus, according to the embodiment shown in FIG. 8, the ring gear 5serves as an inertial mass together with the mass increasing portion 9to suppress vibrations. In this case, as shown in FIG. 9a , the sun gear2 may be connected to the prime mover 7 to serve as the input element,the carrier 5 may be connected to the driven member 8 to serve as theoutput element, and the spring damper 6 may be interposed between thesun gear 2 and the carrier 5. Alternatively, as shown in FIG. 9b , thesun gear 2 may also be connected to the driven member 8 to serve as theoutput element, the carrier 5 may also be connected to the prime mover 7to serve as the input element, and the spring damper 6 may be interposedbetween the sun gear 2 and the carrier 5.

According to the embodiments shown in FIGS. 6 to 9, therefore, a mass ofthe carrier 5 or the ring gear 3 may also be increased withoutelongating an axial length of the planetary unit 1. For this reason, thevibration damping device thus having enhanced vibration dampingperformance may be fitted easily into a powertrain.

What is claimed is:
 1. A torsional vibration damper, having: a planetaryunit that performs a differential action among a sun gear, a ring geararranged concentrically with the sun gear, and a carrier supportingpinion gear interposed between the sun gear and the ring gear in arotatable and revolvable manner; wherein any of the sun gear, the ringgear and the carrier serves as an input element to which torque isapplied, and any of another rotary element serves as an output element;and wherein the input element is connected to the output element throughan elastic member while being allowed to rotate relatively with eachother; the torsional vibration damping device comprising: a vacant areathat exists between an outer circumference of the sun gear and an innercircumference of the ring gear outside of a revolving range of thepinion gears revolved as a result of relative rotation between the sungear and the ring gear, wherein the vacant area is an unused area of thesun gear, in which the pinion gears do not roll; and a mass increasingportion that is formed on the ring gear other than the input element andthe output element within the vacant area in such a manner as toradially protrude from the ring gear.
 2. The torsional vibration damperas claimed in claim 1, wherein the mass increasing portion is formed onthe sun gear.